The invention relates to a safety device between a safety actuator control system and a logic circuit for controlling these actuators. It applies more particularly to the testing of transmission means and systems enabling the application of urgent release signals to a safety actuator. These safety actuators are used, for example, for controlling the emergency shutdown or scram of a nuclear reactor.
It is known that a nuclear reactor, for example, comprises a large number of devices enabling the checking and monitoring of its operation. These devices are called safety actuators. In the case of incidents, it must be possible to release these actuators in an urgent manner, in such a way that their protective action can stop the incident. In nuclear reactors, the values of a certain number of physical magnitudes such as pressure, temperature, neutron flux, etc are measured at a certain number of points by means of transducers. The analog values of these magnitudes are converted into digital values, which are then compared in processing systems with reference values. These processing systems also make it possible to control one or more safety actuators. They normally supply a logic comparison signal which is, for example, of a non-zero value, when the digital values of the physical magnitudes are within a predetermined reference value range and corresponding to the normal operation of the monitored reactor or apparatus. When the physical magnitudes measured by the transducers pass beyond this safety range, the processing and control system or systems supplies logic output signals of e.g. zero value, for each of the measuring values passing beyond the safety range. These logic output signals from the processing system are sequentially applied by communication means which will be described hereinafter to the input of a logic circuit, whose outputs control safety actuators. In general, this logic circuit is designed in such a way that a protective action is initiated when at least half the redundant channels of the communication means apply to at least half the inputs of this logic circuit signals controlling the initiation of protective actions. As stated in French patent application No. 80 25068 filed on Nov. 26, 1980 in the name of the present Applicant, such logic circuits also make it possible to inhibit certain of the transmission channels for performing tests, e.g. circuits or the system located upstream of said channels. These upstream circuits can, for example, be signal amplification and processing chains connected to the aforementioned transducers.
For safety reasons, it is particularly advantageous to release the safety actuator via the logic circuit controlling it, in the case of a failure in the transmission of the logic control signals supplied by the processing and control system to the logic circuit, or in the case of a failure of the said system. At present, no safety device is known which makes it possible to simply and permanently check that the sequential transmission of the signals between a processing and control system and a logic control circuit of a safety actuator takes place without failure and also to check that the processing and control system itself is also suffering from no defect or failure.